Later, after opening the discussion to audience questions, moderator James Moll allowed the Scientology filmmaker to speak. The man launched into a speech -- punctuated by catcalls from some audience members -- which culminated in his declaration that Gibney's film amounts to religious bigotry.

Gibney brushed off the criticism but commented that Scientology has embarked on a campaign of vilification against him which included producing a film that disparaged Gibney's father.

"They do have a reputation for going after people," Gibney told the audience. "It's psychological cruelty and intimidation."

The Scientology protester/filmmaker actually raised one interesting point, asking how audiences can determine whether a nonfiction film is a legitimate documentary versus a smear job. Gibney responded that it's up to audiences to make that determination themselves, and that one factor to consider is the reputation of the person behind the documentary.

In the case of Gibney, he is an Oscar winner and his Going Clear recently won a DuPont Award. The film is based on Going Clear: Scientology, Hollywood and the Prison of Belief by Putlizer Prize winning author Lawrence Wright.

Alex Gibney in a photo from Getty Images

Apart from the Scientology awkwardness, the evening was a pleasant affair, with nominees discussing the challenges they faced to make their films.

E. Chai Vasarhelyi, who co-directed the climbing film Meru with her husband Jimmy Chin, said, "You couldn't pay me to go on a mountain."

The couple joked that Jimmy's desire to continue climbing is an ongoing point of discussion in their marriage, a discussion frequently carried out in public during Q&A's for the film.

Chin said as a filmmaker and climber, he must always balance the degree of risk he is taking. But he said for everyone in life there is a danger of risking too little.

Kapadia, who just returned from Sundance where he served on the World Cinema Documentary committee, spoke about the difficult process of building trust with friends of Amy Winehouse for his documentary Amy.

"No one wanted to talk to me," at first, the director said. He described his film as "almost an investigation to figure out what happened" to Winehouse, who died at 27 after years of drug and alcohol addiction.

​The documentary paints a disparaging picture of Winehouse's father, Mitch, and some others in Amy's camp who appeared more concerned with making money off of the singer than allowing her to deal with her addiction issues.

Amy is the frontrunner for the Academy Award, and has earned more than $8 mil. at the box office in North America alone, a rare achievement for a documentary film.

"Senna was five years of editing. Amy was three years of editing," Kapadia said.

Garbus' film on Nina Simone is a sometimes painful examination of the transcendent power of the artist, who suffered from an undiagnosed bipolar condition for much of her life.

"I have to live with Nina, and that is difficult," Simone says of herself in the film.

The singer died in a sort of self-imposed exile in France in 2003, meaning Garbus did not have the opportunity to interview her for the documentary. But Garbus told the DGA audience she was able, after a lengthy process, to obtain audio recordings Simone did with the co-writer of her autobiography, which offered an intimate glimpse into the singer's mind.

Matthew Heineman, director of "Cartel Land," and Kathryn Bigelow, executive producer of the film, photographed at a screening in Century City, Calif. Credit: Matt Carey

As for Matthew Heineman, director of the visceral Mexican drug war doc Cartel Land, he told the DGA crowd "Restrepo and The Square were big inspirations for me."

One of the most memorable scenes in his film is of drug dealers cooking meth in the hinterlands of Michoacán, Mexico. Heineman said he worked for nine months to try to get access to those clandestine operations.

As night fell, he faced a dilemma about how to light the scene. He wound up doing it with some very modest wattage courtesy of a small flashlight carried by one of the meth dealers.

And he reminded the audience of a point that cannot be repeated too often.